TUESDAY, May 8, 2012 (HealthDay News) -- Older women with the irregular heartbeat known as atrial fibrillation face a 14 percent greater risk of stroke than men with the same condition, Canadian researchers report.
The raised risk remained higher even when women were taking the blood-thinner warfarin (Coumadin) to prevent stroke, the study authors noted.
"Previously, there was a common belief that women were undertreated, and this was the cause for the higher risk of stroke," said lead researcher Dr. Louise Pilote, director of the division of general internal medicine at McGill University and McGill University Health Center in Montreal.
"Our current paper shows that this is not the situation and, compared to men, women have higher risk for stroke regardless of warfarin prescriptions," she said. "This study should alert doctors treating patients with atrial fibrillation that women, especially older women, have a higher risk for stroke compared with men, and therefore sex should weigh in the decision to start a patient on blood-thinners and the dose should be followed closely."
The report was published in the May 9 issue of the Journal of the American Medical Association.
To see if there were differences in the risk of stroke between men and women with atrial fibrillation, Pilote's group collected data on more than 39,000 men and 44,000 women aged 65 and older.
Although both men and women were taking the blood-thinner warfarin, the researchers found more women (5.8 percent) than men (4.3 percent) suffered strokes.
The difference between men and women was particularly strong among those aged 75 and older, where women were more prone to stroke regardless of warfarin use or adherence to taking the blood-thinner, the investigators found.
Atrial fibrillation is a common cardiac arrhythmia that affects an estimated 2.2 million Americans, the researchers noted.
People with atrial fibrillation have a fivefold increase in the risk of stroke compared with the general population, which is why blood-thinners are prescribed for these patients, they explained.
Dr. Gregg Fonarow, a professor of cardiology at the University of California, Los Angeles, said that "a number of recent studies have suggested that women with atrial fibrillation are at even greater risk for stroke than men, and recent updates to stroke risk prediction tools in patients with atrial fibrillation have integrated this information."
The reasons for gender-based differences in stroke risk have not been entirely clear, but differences in use of blood-thinning treatment has been hypothesized.
"While determining the mechanisms accounting for this higher stroke risk in women requires further study, physicians should be aware of this especially high risk of stroke in women and optimize stroke prevention therapies," Fonarow said.
For more on atrial fibrillation, visit the American Heart Association.